Belgian police detained 14 people alleged to have links to al-Qaida in Brussels yesterday as the EU summit got under way. One of those held had made a "martyrdom video", including a farewell message, according to Belgian authorities.

The arrests took place during a series of raids in Brussels and included suspects who had been under surveillance for more than a year and had previously travelled to Afghanistan and Pakistan. The police action came just hours before the heads of 27 countries assembled in Brussels for the summit, although there was no evidence that the meeting itself had been specifically targeted.

During the course of Wednesday night and yesterday morning, about 250 police officers raided 16 locations in the capital and one in Liège. Among items seized, according to police, were computers, data storage equipment and a pistol.

"There was no other choice than to intervene today," federal prosecutor Johan Delmulle told reporters. He said a "martyrdom" video had been found in which the suspect allegedly "said goodbye to his loved ones so as to be able to enter paradise with a clear conscience".

Delmulle said it was unclear where the attack had been planned to take place. He said it was possible that a suicide bombing plan might have been drawn up during visits to Afghanistan and Pakistan. It was not clear if any planned attack was aimed at Europe or elsewhere, he added.

Belgian politicians supported the police action. "It is now clear to all that we were dealing with a real risk," the justice and interior ministers said in a statement. "It is more than likely that an attack in Brussels has been prevented."

Yves Leterme, the prime minister, commended the police action. "It is clear that we have to take the terror threat seriously," he said before the first session of the summit.

No details of the nationalities of those held by police were given but it is understood that they included four Belgians.

The investigation is focusing on individuals linked to Nizar Trabelsi, a 37-year-old Tunisian former footballer sentenced to 10 years in prison in 2003 in Belgium for planning to a drive a car bomb into the cafeteria of the Kleine Brogel airbase, where about 100 American military personnel were stationed.

Almost exactly a year ago, Belgian police arrested 14 people alleged to be extremists planning to free Trabelsi. At the time, the government also claimed that it had information suggesting the "preparation of an attack". Trabelsi is also said to have had links with extremist groups in Britain and France.

British counter-terrorism officials said last night that they were working with Belgian and other European security services to try to establish whether the EU summit was the target. They said they were keeping an "open mind". There was no suggestion the target was a British one.

The summit went ahead yesterday under heavy security, with police helicopters flying overhead.

Claude Moniquet, the president of a Brussels-based thinktank, the European Strategic Intelligence and Security Centre, said that those detained included Moroccan-born Malika el-Aroud, a 48-year-old Belgian who writes online in French under the name of Oum Obeyda.

In an interview with the New York Times last May, she said: "It's not my role to set off bombs, that's ridiculous. I have a weapon. It's to write. That's my jihad. You can do many things with words. Writing is also a bomb."